Python print function keyword arguments

The Python print function is one of the first one folks learn about, since it’s part of the “Hello World” program. It’s often presented with its most basic usage, by passing a single argument to it:

print("Hello World")

Simple, and readable.

However, I recently rediscovered its keyword arguments, especially the end one, that defaults to \n (newline character), which is added at the end of whatever you want to print. That’s why when you call the above snippet multiple times, you’ll see each string printed on a new line, as opposed to have them on the same.

The problem

When running a long command, if you want to print the progress of the command, you might be tempted to do:

def do_thing_over_many_entries(entries):
    total = len(entries)
    print(f"Starting processing {total} entries")
    for index, entry in enumerate(entries, 1):
        print(f"Processing entry {index}/{total}")
        # Do the thing
    print("All done")

This will print a wall of text, e.g.

Starting processing 4000 entries
Processing entry 1/4000
Processing entry 2/4000
Processing entry 3/4000
...
Processing entry 4000/4000
All done

Which might be a bit disruptive as it’ll fill up your terminal.

Solution wih standard library

Using the end keyword argument is useful, you can pass carriage return \r to instead update the same line in place:

def do_thing_over_many_entries(entries):
    total = len(entries)
    print(f"Starting processing {total} entries")
    for index, entry in enumerate(entries, 1):
        print(f"Processing entry {index}/{total}", end="\r")        # Do the thing
    print("All done")

Which will update the “Processing entry…” line as it goes:

Starting processing 4000 entries
Processing entry 4000/4000
All done

Solutions with 3rd party packages

This is a simple example with vanilla Python, but other libraries are providing higher abstractions for this kind of operation:

• Rich
• TQDM

If you can afford to add a dependency to your project, check these out.